Multi-application lubricants that are used to lubricate the moving parts of off-highway mobile equipment such as farm tractors, off-highway equipment, and construction equipment are designed to lubricate the transmissions, differentials, final-drive planetary gears, wet-brakes, and hydraulic systems of said equipment. Therefore these fluids must meet many performance requirements including water tolerance, copper corrosion resistance, wet-brake friction, wear resistance, and high energy clutch transmission performance. Lubricants such as tractor lubricants are often exposed to large contaminant amounts of water. The contaminant amounts of water are believed to be caused by ingress of water through equipment seals during operation. The water may form a second layer in the lubricant. Typically, to reduce the formation of the second layer, emulsifiers are employed. If the water is not emulsified into the lubricant, the water may cause additional difficulties such as copper corrosion from copper containing parts of a wet-brake, a transmission, a hydraulic, a final drive, a power take-off system. These parts are typically lubricated by a single lubricant supplied from a common sump.
European Patent Application 1 191 087 A discloses a method of protecting a copper-containing metal from loss of copper when in contact with a functional fluid composition containing water, said method comprising employing in said functional fluid an oil-soluble dimercaptothiadiazole compound or derivative thereof in an amount sufficient to protect against loss of copper. There is no disclosure of emulsifying water in the lubricant.
In addition, many lubricants contain zinc dialkyldithiophosphate (ZDDP) antiwear agents. In the presence of water, the ZDDP may break down, resulting in release of more labile (or reactive) sulphur. The labile sulphur may increase copper corrosion. Additionally, as the ZDDP antiwear agent decomposes increased wear may occur due to the presence of reduced amounts of antiwear agent.